The present invention relates to the control of a gas turbine power plant and, more particularly, to means for controlling turbine acceleration in a manner which substantially decreases the possibility of flameout. The present invention is equally suitable for employment in the primary control system of a gas turbine implemented power plant or in a local maintenance or backup controller therefor.
In the local maintenance controller described in the above-referenced U.S. Pat. application No. 476,182, or in the primary control system for a gas turbine implemented power plant described in the above-referenced U.S. patent application No. 82,470, ignition is accomplished in the turbine combustor as a result of a fixed energy input. More specifically, fuel flow for ignition purposes is initiated at a fixed fuel valve minimum setting and pressure. This fixed energy input at ignition results in a quantum jump in turbine speed at ignition.
With a turbine control system of the types referenced above, i.e., the control system develops a fuel quantity control or demand signal output (or CSO) which is initially speed dependent through at least ignition, the CSO would be negative or call for a fuel valve position which is less than its fixed minimum position at ignition. As a result increased fuel delivery and acceleration of the turbine will not commence until the speed reference signal catches up with turbine speed. The length of time required for this to happen is often undeterminable and a function of ambient conditions.
However, it may happen that with a given set of ambient comditions, the period in which the CSO is negative may exceed the period of atomizing air time, the period of time in which the supply of air for fuel atomizing purposes will be exhausted. When this occurs, flameout or ignition failure can and often will result.
Consequently, there exists a specific need to provide a means of avoiding flameout in gas turbine control systems which employ a fixed energy ignition input or in which ignition occurs at a fixed, minimum fuel valve setting coupled with an initial speed tracking mode of operation through at least the ignition stage.